This invention relates to a method for supporting a fiber optic cable from a messenger strand and the provision of an assembly therefor. Specifically, the invention relates to a sheath support assembly which loosely contains a tension sensitive fiber optic cable which has a coefficient of linear expansion substantially less than that of the messenger strand and sheath support assembly.
When conventional electrical cable is suspended between upright support poles, a messenger strand, which is usually constructed of metal, is used to support the transmission cable. This poses no problem when the transmission cable is itself metallic in nature, as the respective coefficients of linear expansion of the messenger cable and the transmission cable are substantially similar. As changes in atmospheric conditions occur, such that the cables heat and cool, the cables elongate and contract with substantially equal changes in length. Metallic messenger strands and transmission cables may elongate and contract five inches or more over a span of 200 ft. when subjected to temperature extremes.
Modern communication systems are more and more relying on fiber optic techniques in place of conventional electrically conductive transmission cables. Briefly, a single fiber optic cable can transmit several hundred times more voice and data information than a similarly sized conventional metallic transmission cable. Rapid firing laser pulses are used to transmit information over a fiber optic cable. A fiber optic cable, however, does not exhibit the same elongation and contractive responses as does a conventional electrical transmission cable or a conventional metallic messenger strand. A fiber optic cable is substantially impervious to elongation and contraction when subjected to temperature variations. PG,3 Additionally, a fiber optic cable is generally limited to bearing a load of 500 pounds.
Conventional support techniques are therefore inappropriate to aerial suspension of fiber optic cables. Were a fiber optic cable to be tightly bound to a messenger strand, as is a conventional transmission cable, the tension applied to the fiber optic cable as the messenger strand expanded, thereby reducing or eliminating its support, would initially distort the fiber optic cable and eventually would cause the fiber optic cable to break under its weight and the weight of a messenger strand.
An object of the instant invention is to provide a support assembly for supporting a fiber optic cable from a conventional, metallic messenger strand.
Another object of the invention is to provide a support assembly for a fiber optic cable where the coefficient of linear expansion for the fiber optic cable and the coefficient of linear expansion for the messenger strand are substantially unequal.
A further object of the invention is to provide a method of supporting a tension sensitive cable from a messenger strand where the messenger strand has a coefficient of linear expansion which substantially exceeds that of the tension sensitive cable.
The instant invention includes a sheath support assembly which includes an elongate, flexible containment means having a passage extending therealong. A portion of the passage receives a fiber optic cable. The cable is loosely and slideably received within the passage. Another portion of the passage receives a messenger strand to support the assembly. The containment means has an entry means extending along its length for allowing introduction of the cable and the strand to the containment means. Means are provided for securing the containment means with the messenger strand received therealong.
These and other objects and advantages of the instant invention will become more fully apparent as the description which follows is read in conjunction with the drawings.